Ralph is chosen leader right away. He is the one who blows the conch, so he is considered leadership material by the boys.

None of the boys could have found good reason for this; what intelligence had been shown was traceable to Piggy while the most obvious leader was Jack. (ch 1)

Ralph has the conch, and is the one who got them all together—accidentally or not. Also, Ralph is good-looking and has a “stillness” that seems to inspire confidence.

Unfortunately, Ralph does not desire to be a leader like Jack, and does not make much of an effort to think things through. He feels himself losing control almost immediately, because he can’t get the boys to listen to him.

Ralph looked at them with unwinking eyes. Simon turned away, smearing the water from his cheeks. Ralph reached inside himself for the worst word he knew.

“They let the bloody fire go out.” (ch 4)

Ralph’s lack of leadership skills coupled with Jack’s barbarism leads to the group splitting, and the deaths of Simon and Piggy. Ralph was aware that he should have been a better leader, he just did not know how to do it.